This application is based upon and claims the benefit of Japanese Patent Application No. 2001-28459 filed on Feb. 5, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic control system and method that are capable of detecting microcomputer malfunction by monitoring operations of one microcomputer by another one. Especially, the present invention relates to a throttle control microcomputer and method that conduct electronic throttle control of an engine of a vehicle.
2. Related Art
Electronic control systems have the monitoring function to detect a microcomputer malfunction by monitoring operations of a plurality of microcomputers against one another. For example, an electronic control system of a vehicle has an engine control microcomputer for executing engine control (spark ignition, fuel injection or the like) and a throttle control microcomputer for executing electronic throttle control. A monitoring program is provided in the engine control microcomputer, thereby to monitor the throttle control microcomputer in the engine control microcomputer. For instance, in U.S. Pat. No. 6,230,094 (JP-A-11-294252), an engine control microcomputer monitors a throttle control microcomputer. When the engine control microcomputer detects malfunction of the throttle control microcomputer, the engine microcomputer resets the throttle control microcomputer and executes the throttle control in place of the throttle control microcomputer.
In order to increase reliability and safety of the throttle control microcomputer, it is desired to monitor operations of the monitoring program itself. Therefore, in JP-A-11-294252, a watch-dog pulse is outputted periodically, and the watch-dog pulse is inputted to a watch-dog timer. Thus, the monitoring program is watched. It is, however, required to provide a hardware IC to watch the monitoring program.
It is therefore an object of the present invention to provide an electronic control system, which is capable of obviating the above problem.
It is another object of the present invention to provide an electronic control system, which is capable of attaining a monitoring function of a microcomputer.
According to the present invention, a first microcomputer is programmed to control a first object such as a fuel injection or ignition timing of an engine. The first microcomputer has a monitor program for checking malfunction of a second microcomputer periodically. The second microcomputer is programmed to control a second object such as a throttle driving motor. The first microcomputer comprises a timer and a timer setting unit. The timer increases or decreases time count in proportion to time, and switches the output logic level of its port when the time count reaches a predetermined time. The timer setting unit sets a new time count in place of the time counted by the timer when an operation of the second microcomputer is normal and the monitor program is normal.